Ultrafast dephasing of continuum transitions in bulk semiconductors

Arlt, Sebastian; Siegner, U.; Kunde, J.; Morier‐Genoud, F.; Keller, U.

doi:10.1103/physrevb.59.14860

“…which is different from t À1 G n 0:3 eh , which was found for bulk GaAs by the same group [2]. The results for bulk GaAs were confirmed by us [3] and others [5]. In this article, we present data on GaAs quantum wells under conditions which are comparable to bulk.…”

supporting

confidence: 70%

Dephasing Due to Carrier-Carrier Scattering in 2D

Hügel

¹

,

Heinrich

²

,

Wegener

³

2000

phys. stat. sol. (b)

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We show that there is no significant difference in the dephasing due to carrier±carrier scattering between bulk GaAs and GaAs quantum wells. This is in contrast to previous experimental work with worse dynamic range.Carrier scattering and screening of the Coulomb potential in two dimensions (2D) are often believed to be quite different from those in three dimensions (3D). Our intuition tells us that carriers in 2D cannot move in one spatial direction therefore one is tempted to argue that screening of the Coulomb potential will be less effective in 2D. This in turn should strongly influence the carrier±carrier scattering rates via the carrier scattering cross section. Early experiments by Shank and co-workers [1] on quasi-2D GaAs quantum well structures indeed indicated that the decay time t of the coherent four-wave mixing (FWM) signal has a scaling with the optically excited carrier density n eh according to t À1 G n 0:55AE0:04 eh

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“…Early experiments by Shank and co-workers [1] on quasi-2D GaAs quantum well structures indeed indicated that the decay time t of the coherent four-wave mixing (FWM) signal has a scaling with the optically excited carrier density n eh according to t À1 G n 0:55AE0:04 eh which is different from t À1 G n 0: 3 eh , which was found for bulk GaAs by the same group [2]. The results for bulk GaAs were confirmed by us [3] and others [5]. In this article, we present data on GaAs quantum wells under conditions which are comparable to bulk.…”

mentioning

confidence: 58%

Dephasing Due to Carrier–Carrier Scattering in 2D

Hügel

¹

,

Heinrich

²

,

Wegener

³

2000

phys. stat. sol. (b)

View full text Add to dashboard Cite

We show that there is no significant difference in the dephasing due to carrier±carrier scattering between bulk GaAs and GaAs quantum wells. This is in contrast to previous experimental work with worse dynamic range.Carrier scattering and screening of the Coulomb potential in two dimensions (2D) are often believed to be quite different from those in three dimensions (3D). Our intuition tells us that carriers in 2D cannot move in one spatial direction therefore one is tempted to argue that screening of the Coulomb potential will be less effective in 2D. This in turn should strongly influence the carrier±carrier scattering rates via the carrier scattering cross section. Early experiments by Shank and co-workers [1] on quasi-2D GaAs quantum well structures indeed indicated that the decay time t of the coherent four-wave mixing (FWM) signal has a scaling with the optically excited carrier density n eh according to t À1 G n 0:55AE0:04 eh which is different from t À1 G n 0:3 eh , which was found for bulk GaAs by the same group [2]. The results for bulk GaAs were confirmed by us [3] and others [5]. In this article, we present data on GaAs quantum wells under conditions which are comparable to bulk. We find no significant difference between 3D and 2D.The experiment on quantum wells is very closely similar to our recent experiments on bulk GaAs [3]. The laser spectrum of the nearly transform-limited 11 fs optical pulses is centered slightly above the 2D band edge of the 11.6 nm wide GaAs quantum well sample [4]. In order to compare our 2D with our 3D experiments (E) [3] and theory (T) [4] we plot the decay time t of the time-integrated FWM signal as a function of the optically excited carrier density in Fig. 1. The sheet densities for GaAs quantum wells and the volume densities for bulk GaAs, can simply be related by the QW thickness L z via the relation n 2D eh L z n 3D eh , with L z 11:6 nm. Obviously, all data points ± experiment/theory and 3D/2D ± fall together. Note, that we use a logarithmic scale for n eh . From this plot we conclude that there is no significant difference in the dephasing due to carrier±carrier scattering between 3D and 2D. This is in sharp contrast to previous work [1]. Thus, the following questions arise: (i) How does the quality of our experimental data compare to that of previous work? (ii) Are the excitation conditions (3D/2D) comparable? (iii) What is the role of the second subband? (iv) Is there a dependence on quantum well width?We now address these issues (i) to (iv). (i) How does the quality of our experimental data compare to that of previous work? The dynamic range in the carrier densities investigated spans two orders of magnitude for both, our experiments on bulk GaAs and our experiments on GaAs quantum wells. In Ref.

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“…One study [19] found that the dephasing rate increased by less than 40% over a factor of ten increase of density from 10 16 -10 17 cm −3 , corresponding to a power law of 1/τ ∝ n 0.15 ; another study [20] found about 50% increase over the same range. The absolute values of the dephasing in these studies were also consistent with the quantum Boltzmann theory.…”

Section: Results For Electron-hole Plasmamentioning

confidence: 94%

“…This formula gives τ 25 fs for electrons in GaAs at room temperature and τ 200 fs at for electrons in GaAs at 4 Kelvin. Arlt et al [19] found an average low-density dephasing time of around 15 fs at room temperature, while Hügel et al [20] found an average dephasing time of around 25 fs. Both are much shorter than the minimum electron-phonon scattering time of around 150 fs [21,22].…”

Section: Results For Electron-hole Plasmamentioning

confidence: 97%